The use of rapid on-site testing to assess a condition, situation or problem arises in a number of areas such as diagnostics, environmental monitoring and testing, monitoring of physical, biological or chemical phenomena (such as the formation of physical aggregates of particles or aggregation due to chemical forces, such as protein-protein interactions), water contamination and food contamination. Current methods and devices available for such testing are often costly and cumbersome to use at the point of care or at the site of interest, due to the need for precise metering of the sample to be tested. Accordingly, there is a need for cost-effective, compact, rapid testing devices that eliminate the difficulty of having to measure precise, reproducible amounts of a sample that is to be tested on site. In one application, a simple, low cost, at-home device for testing blood hematocrit can be of significant benefit to patients with anemia, given the cost of other devices on the market that require an electronic meter.